The present invention generally relates to the removal of metallic contaminants from petroleum fractions. Specifically, the present invention relates to the removal of complex organo-metallic compounds, for example, of the porphyrin type, and particularly those compounds containing nickel and vanadium from residua by deasphalting. In petroleum processing operations such as catalytic cracking the presence of these metallic contaminants in the petroleum feed, e.g., in a deasphalted oil, leads to rapid catalyst contamination by metals causing an undesirable increase in the hydrogen and coke makes, a loss in gasoline yield, a loss in conversion activity and a decrease in the catalyst life. The metal contaminant concentration generally is higher in the heavier feedstocks. Thus, the removal of metal contaminants is becoming more important as increasingly heavy feedstocks are being refined and as additional efforts are being directed at upgrading the residual petroleum fractions.
In the past, efforts have been directed at the removal of metal contaminants from petroleum fractions by a variety of methods including deasphalting processes, hydrotreating processes and HF extraction. U.S. Pat. No. 2,926,129 is directed at the removal of organometallic compounds and the deasphalting of a petroleum fraction by heating the petroleum fraction at a temperature of 650.degree.-850.degree. F. for 0.1 to 5 hours after which the fraction is contacted with an acidic material soluble in the petroleum fraction, such as HCl, to coagulate the metallic contaminants. A sludging component, such as a liquid SO.sub.2 is then added to the petroleum fraction at the rate of 0.1 to 3 volumes of SO.sub.2 per volume of oil to promote precipitation of the asphaltene. A solvent also is added to the fraction preferably at the rate of 0.1 to 10 volumes per volume of oil to separate the asphaltene sludge fraction in a fractionating tower operated at temperatures of 30.degree. to 300.degree. F. and pressures of 25 to 300 psig. This patent also discloses in a table in column 5 that a less effective reduction in metals content in the recovered oil may be accomplished utilizing the solvent and liquid SO.sub.2, without the acid. Use of the process described in this patent is not desirable since relatively large quantities of sulfur dioxide in the liquid state are required, which necessitates operating at high vessel pressures if high temperatures are used and may necessitate the removal of the SO.sub.2 from the recovered oil and from the sludge. Moreover, addition of an acid, such as HCl would require that the processing equipment be acid resistant. Furthermore, the pressure of halogen compounds in the system increases the potential for downstream corrosion, particularly if water should be present. In addition, the presence of acidic compounds in the recovered oil would be injurious to catalysts used in subsequent processing.
U.S. Pat. No. 3,294,678 is directed at a deasphalting process for the separation and removal of asphaltenic material including organo-metallic complexes of nickel and vanadium which comprises treating the petroleum fraction with an alkalinous bisulfide or bisulfite in aqueous solution under a pressure in the range of 150 to 2000 psig in the presence of sufficient sulfur dioxide such that the partial pressure of the sulfur dioxide is within the range of about 150 to about 1500 psig. The asphaltenic material including organo-metallic compounds is converted into a water-soluble sulfonic acid salt which is subsequently extracted. This process is not desirable because of the additional steps of separating the water fraction from the petroleum fraction and separating the sulfonic acid salts from the asphaltenic material.
U.S. Pat. No. 2,969,320 discloses a method for removing tetraethyl lead from gasoline and other hydrocarbon liquids by injecting sulfur dioxide into the liquid to form an insoluble lead sulfide which may subsequently be removed by filtration. This method does not disclose or suggest removal of metals such as nickel and vanadium from petroleum fractions by heating in the presence of sulfur dioxide prior to deasphalting.
U.S. Pat. No. 3,095,368 describes a method for selectively removing iron, nickel and vanadium from an asphaltic petroleum feedstock by deasphalting the oil and subsequently contacting the oil with a mineral acid to coagulate the metallic compound. The metallic compounds are then separated. This process requires the use of mineral acids which are corrosive and requires additional processing steps.
In a paper presented at the 1980 meeting of the Division of Petroleum Chemistry of the American Chemical Society, Bukowski and Gurdzinska disclosed a method for reducing the adverse catalytic effect of metal contaminants present in the distillate from atmospheric residuum. The method included the heat treating of the atmospheric residuum in the presence of cumene hydroperoxide (CHP) for up to six hours at 120.degree. C. This step increased the distillate fraction obtained from the atmospheric residuum feed and decreased the metals content of the distillate which subsequently was used as feed for a catalytic cracking unit. This procedure is not advantageous due to the relatively high cost of the CHP required and the long treatment times involved.
British Patent Application No. 2,031,011 describes a method for reducing the metals and asphaltene content of a heavy oil by hydrotreating the oil in the presence of a catalyst including a metal component from Group Ib, IIb, IIIa, Va, VI, and VIII of the Periodic Table followed by deasphalting. This process is not preferred since relatively large quantities of hydrogen are required in addition to a large investment in hydrotreating reactors and process equipment.
Accordingly, it is desirable to provide a process which reduces the metals concentration in a petroleum fraction to sufficiently low levels without the addition of large amounts of acidic materials. It also is desirable to provide a process in which the metals content of a petroleum fraction is reduced without the addition of a halogenated compound.
It also is desirable to provide a process which does not require the further addition of a metal rejection agent to the deasphalting zone.
It is also advantageous to provide a process which will reduce the metals concentration in the petroleum fraction without an excessive amount of equipment and without the addition of a large number of additional processing operations to recover the metals rejection agent.